Glossary

Glossary terms beginning with: M

Small perforations usually confined to genital plate 2 which mark the external opening to the water vascular system. These are also known as hydropores.

madreporite plate

The genital plate that lies at the apex of interambulacral zone 2 and which is pierced by madrepores. It is usually the largest of the genital plates.
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mamelon

A rounded, ball-like articulation surface forming the top of a tubercle and the bearing surface on which the spine rests. The mamelon may be perforate (with a central pit) or imperforate (as in this picture).
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marginal (fasciole)

A fasciole band that runs around the ambitus of the test, passing beneath the periproct at the posterior.
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membranous gaps

Large gaps between plates of the corona that are filled with soft-tissue membranes in life. These are found only in the echinothurioids.
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meridoplacous

An interambulacral plating arrangement in which the first (primordial) plate (red) is followed by a single sternal plate (2b: green). The second sternal plate (2a: green) is paired with the first episternal plate (3b: blue)
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